1. Field of the Invention
The present invention relates to a colouring composition for colouring polyvinylchloride. The term polyvinylchloride also includes copolymers of vinylchloride and otherwise modified polyvinylchloride.
For colouring polymers, colouring pigments are used on a large scale.
2. Description of the Prior Art
It is known e.g. in the art to manufacture by injection moulding plastics articles in various different colours, as required by the customers. Examples of such articles are pipe fittings, covers, boxes etc.
It is also known in the art to extrude thermoplastics pipes which have to meet different demands, with very particular colours, in order to avoid any risk of exchanging plastics pipes, to be used for a certain aim, with other pipes, which would be absolutely unsuitable for that aim. So, for instance, a plastics pipe for transporting water is given a colour differing from the colours used for pipes being employed for transport of gases.
Said colouring compositions present the disadvantage, that the great fineness of the colouring particles may be a nuisance, whilst furthermore, handling the empty packages of such colouring pigments requires much labour, so that transporting said empty packages and preventing the hindrance by fine dye particles, should be restricted to a minimum. It is not always possible to choose pigments without toxic character, so that there is always danger of contamination by handling such pigments.
Efforts have been made to obviate these disadvantages by providing the mixers, in which plastics are mixed with colouring pigments, with metering devices, metering the material on a volume- or on a weightbasis, thus allowing the use of containers with colouring pigments.
Metering devices allowing an accurate control of the quantity of colouring pigments to be dispensed are, however, extremely expensive; also measures have to be taken to avoid dusting.
Efforts have also been made to admix the colouring pigments with additives in the form of molten fatty acid amides and to cast the liquid composition into moulds, whereupon the moulded articles obtained after solidification may be used for forming a mixture with plastics, or to grind the moulded articles and to use the granulate particles as an additive for the thermoplastics to be coloured. The latter method is very inconvenient in that fatty acid amides melt at rather high temperatures, thus causing the risk of impairing the properties of organic colouring pigments. Moreover, the high melting points of the additives complicate proper dispersion of colouring pigments in the thermoplastics.